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FL inverter
By commanda, Section Diaries Posted on Fri Jun 3rd, 2005 at 06:25:48 AM MST
minimal parts count - pre-wound transformer

This is basically the fly-back circuit I've used numerous times to power lcd backlights. The switching device is an n-channel mosfet. I used an MTP3055 because I had some handy. The transformer is a small ferrite from a junked ATX power supply. The core is 20x18x5 mm, driving a 15 watt tube. Use the winding with the highest resistance as the secondary. R1 is select on test. The diode should be a high speed type, if possible. The capacitor is also select on test. If you can hear it whistling, you probably need a smaller capacitor.
R2 is required, because when the tube fires, the gas ionises, and becomes conducting. R2 limits the pulse current. Performs a similar function to the ballast transformer in a standard fluoro.
Transformer phasing is important. It will work one way, but not the other.

PDF of circuit
Photos of prototype, and test results with other tubes and transformers coming.
Amanda

FL inverter | 26 comments (26 topical, 0 editorial)

Re: FL inverter (3.00 / 0) (#1)
by jacquesm (j@ww.com- I run a whitelist, add 'stjoes' to msg) on Fri Jun 3rd, 2005 at 10:45:00 AM MST
(User Info) http://www.greenbits.com/

that's so small you might actually be able to get it hidden away in the lamp socket... does it get warm ?
www.greenbits.com

Re: FL inverter (3.00 / 0) (#2)
by commanda (alwynne at unwired dot com dot au) on Fri Jun 3rd, 2005 at 04:18:21 PM MST
(User Info)

Running the 15 watt tube, with the mosfet on a heatsink, is only a couple of degrees temperature rise. Got to run it for a while with no heatsink and measure the temp.
Might xmas tree it onto a small flat piece of aluminium to act as a small heatsink, and physically hold it together.

I've also got some 4foot tubes; got to test with them yet also.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#3)
by whatsnext on Fri Jun 3rd, 2005 at 06:14:53 PM MST
(User Info)

Amanda, What frequency do you think this circuit would operate at? Also, I found a slavage seller that has a bunch of the Phillips 13 watt mini FL bulbs for something like 25 cents each. Do you think a circuit like yours will work with a mini FL?
Thanks, John......

Re: FL inverter (3.00 / 0) (#4)
by commanda (alwynne at unwired dot com dot au) on Fri Jun 3rd, 2005 at 09:49:41 PM MST
(User Info)

I'm running it off 24 volts. The frequency varies with voltage. At 20-24 volts, roughly, it's just in the audible range (20KHz). As the voltage climbs towards 28 volts, it becomes inaudible. Frequency would vary with the mosfet and the transformer used.

I've tried with a couple of 12 inch, 8 watt tubes, and have difficulty getting them to fire properly. With another circuit, more complex, pwm drive like the 555 circuit that has been discussed on here, same problem. Tried it with 2 of them, same result. Tried another, bigger transformer, same. These tubes were manufactured by Crompton.

If I could, I'd get one or two of the salvage tubes & try them first.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#8)
by BT Humble (bt_humble@bigpond.com) on Sun Jun 5th, 2005 at 04:39:27 PM MST
(User Info) http://www.humbletown.org

... I found a slavage seller that has a bunch of the Phillips 13 watt mini FL bulbs for something like 25 cents each. Do you think a circuit like yours will work with a mini FL?

Do you mean a straight tube, or the Compact Fluorescent style? I can't see any reason why it wouldn't drive a 13W tube if it'll drive a 15W one.

BTH

[ Parent ]

Re: FL inverter (3.00 / 0) (#9)
by whatsnext on Sun Jun 5th, 2005 at 08:53:39 PM MST
(User Info)

BTH, These are the bulbs that are designed to fit into the small FL fixtures like porch light. They are about 12" long before being folded once. Including the little two prong ceramic base they are about 7" long. They are about the same dia as most other CFLs. I think they are rated at 13 or 15 watts. The ballest is built into the fixture for these bulbs. The reason I like them is that they have a real pleasing color. Much cooler than the blue/white of other bulbs. And, of course, the price is right.
John.......

[ Parent ]

Re: FL inverter (3.00 / 0) (#10)
by commanda (alwynne at unwired dot com dot au) on Sun Jun 5th, 2005 at 09:13:43 PM MST
(User Info)

STOP NOW.

CFL's are a different beast altogether.

These inverter circuits are for running the normal fluorescent tubes which have 2 pins each end for the filament. The standard housing will have a starter, and a ballast transformer.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#11)
by whatsnext on Sun Jun 5th, 2005 at 09:59:26 PM MST
(User Info)

Oh bummer but thanks. I guess I should start looking for a CFL circuit or just gut one and try to figure it out myself.
John.......

[ Parent ]

Re: FL inverter (3.00 / 0) (#12)
by RP (russp located-at fidnet (dot) com) on Sun Jun 5th, 2005 at 10:22:01 PM MST
(User Info)

Wait a minute. It sounds like he's got the CFL bulb only. If that's the case then the inverter should work fine. Amanda, were you thinking he was going to drive the CFL ballast and starter too?

[ Parent ]

Re: FL inverter (3.00 / 0) (#13)
by BT Humble (bt_humble@bigpond.com) on Sun Jun 5th, 2005 at 10:42:31 PM MST
(User Info) http://www.humbletown.org

Wait a minute. It sounds like he's got the CFL bulb only. If that's the case then the inverter should work fine. Amanda, were you thinking he was going to drive the CFL ballast and starter too?

If it was just the tube with no ballast, it should have 4 pins on the base (ie. start and end connection for 2 separate filaments).

BTH

[ Parent ]

Re: FL inverter (3.00 / 0) (#14)
by commanda (alwynne at unwired dot com dot au) on Sun Jun 5th, 2005 at 10:53:24 PM MST
(User Info)

Conflicting data here. He says the ballast is built into the base, but then his tube only has 2 prongs.

Now I'm confused.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#15)
by whatsnext on Mon Jun 6th, 2005 at 06:42:36 AM MST
(User Info)

I might be confused also. I thought there was only two pins. I'm at work now but as soon as I get home I'll check again.
John..........

[ Parent ]

Re: FL inverter (3.00 / 0) (#16)
by commanda (alwynne at unwired dot com dot au) on Mon Jun 6th, 2005 at 03:16:33 PM MST
(User Info)

I think I know what he's got. It's like the tubes used for backlighting laptop displays. It's a cold cathode fluoro tube, ccfl, as against a compact fluoro, cfl.

To me, a cfl is a fluoro tube and integrated ballast (actually a sophisticated inverter) that has a base the same as a normal incandescant bulb.

All these inverter circuits should drive a ccfl just fine.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#17)
by whatsnext on Tue Jun 7th, 2005 at 07:52:49 PM MST
(User Info)

OK Amanda,
The bulb in question says Phillip mexico PL-S(or 5) 13W/27. The little base has 6 and E heat stamped into it's base which is plastic not ceramic. It only has two prongs. I pulled the porch fixture apart to see what's inside. One of the 110VAC leads is attached to one of the lamp prongs. The other one goes into what looks like a choke the other lead of which then goes straight to the bulb, I think. The 'choke' says:Quality Flourescent, Lamp Ballasts since 1939 and Cat, CU 452, 12-13-14-15-18-20-22W, 120V 60HZ .35A.
Does this help?
John........

p.s. The bulb looks like the old style CFL bulb but without any of the base. Two staight tubes with a little passageway between the tubes. Oh, and the bulb is non-polarized.

[ Parent ]

Re: FL inverter (3.00 / 0) (#18)
by commanda (alwynne at unwired dot com dot au) on Tue Jun 7th, 2005 at 10:07:55 PM MST
(User Info)

I did a Google; can confirm it's an "S", not a five, but no other information.

Going by your description of the ballast choke, I'd say the tube should work just fine with any of the inverters published.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#19)
by whatsnext on Wed Jun 8th, 2005 at 08:25:36 AM MST
(User Info)

Amanda, So is the ballast really just a choke? And if so what does a choke do to make the bulb work? I always thought ballasts had a lot more wires coming out of them.
Thanks, John........

[ Parent ]

Re: FL inverter (3.00 / 0) (#20)
by commanda (alwynne at unwired dot com dot au) on Wed Jun 8th, 2005 at 03:38:19 PM MST
(User Info)

In a common, old style, fluorescent tube, yes the ballast is just a choke. When the tube fires, the gas inside ionises, and becomes conducting. The choke limits the current that can flow through the ionised gas to dI/dT. Energy is stored in the choke and released on the next AC cycle. Because the impedance of the mains is effectively zero, without the choke, the ionised tube would appear as a near dead short across the mains without the choke.

I made a post about a week back, "heads up", in which I advised that a small resistor in series with the tube may be necessary with some inverters.

It is unfortunate that the term "electronic ballast" has come into common use. The mass produced cfl lamps have a rectifier and inverter built into them, and called "electronic ballast". I have seen these lamps run off an inverter from 12 volts, but you have to rectify the high voltage, and regulate it to about 350 volts.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#5)
by commanda (alwynne at unwired dot com dot au) on Fri Jun 3rd, 2005 at 10:38:14 PM MST
(User Info)

Photo of prototype. 1" x 1" aluminium angle, just over 3 inches long. Gets to 45 deg C (in a sealed box) running a 15 watt tube off 28 volts with a dc input current of 0.47 amps.

Amanda

Re: FL inverter (3.00 / 0) (#6)
by zap (bell47g5a at comcast dot net) on Fri Jun 3rd, 2005 at 11:48:43 PM MST
(User Info)

Amanda in the past I've looked at every FL inverter post I could find and have always wanted to ask why everyone seems to use the 555 based circuits when smaller less complicated(and I assume cheaper)circuits like yours exist. Are the 555 type better at handling higher current? More efficient? Or is it something else?

I use the inverter and bulb off a scanner like this one and a 12 volt battery for a reading light.

Unfortunately I believe I toasted one of the transistors in this one a few weeks ago when I had a 110v CFL go out so I decided to see if this inverter would light that bulb up. It did, not as bright as when hooked to 110v. I decided to hook it to the pedal genny to see how bright I could get it... Doh! I think it probably gave up the ghost at around 20 volts.

zap

Re: FL inverter (3.00 / 0) (#7)
by commanda (alwynne at unwired dot com dot au) on Sat Jun 4th, 2005 at 01:20:30 AM MST
(User Info)

I found it hard to get consistent current & brightness with varying battery voltage. A 24 volt battery can be expected to go from 20 volts flat to 30 volts at full charge current.

My circuit is very stable in this regard. Only the frequency seems to vary with voltage.

I think choice of fet (gate switch-on voltage) would be critical to get this circuit working on 12 volts. I've previously used bipolar transistors, in a TO-92 case, running off 9 or 12 volts to power lcd backlights. But thats a very low power level.

I expect, though haven't tested it, that this circuit would work well with a TIP41C, after choosing the right value of base resistor.

One last point I noticed; it takes a second or two for the tube to initially fire, after switch on, during which the current draw is about 1.5 amps.

Amanda

[ Parent ]

Re: FL inverter (3.00 / 0) (#21)
by dinges on Wed Jul 26th, 2006 at 09:19:46 AM MST
(User Info)

Zap,

Two days ago I took an old scanner apart and it seems to have EXACTLY the same inverter board in it. I only have one question: do you drive it with 5V or 12V?

I'm not sure whether it needs 5V or 12V. Wasn't easy to retrace on the PCBs anyway.

[ Parent ]

Re: FL inverter (3.00 / 0) (#24)
by zap (bell47g5a at comcast dot net) on Mon Sep 4th, 2006 at 07:47:18 PM MST
(User Info)

Hey Peter, I hope you see this reply.
I have a few of these inverters out of scanners, only one has shown up that wasn't 12v, it was 24v. I found the voltage listed on the main board for the first one (that I toasted). I found out the 24v by hooking the inverter to my pedal generator and pedaling till the bulb went to full brightness.

zap
[ Parent ]

Re: FL inverter (3.00 / 0) (#25)
by dinges on Mon Sep 4th, 2006 at 09:03:14 PM MST
(User Info)

Very nice... They apparently also exist in a 24V version. Could be handy for those with a 24V system. I'd definitely would like a few of the 24V kind.

I also understand that Commanda is at the moment working on (C)FL inverters for the BTHumble project in Fiji. I hope something comes out of it that's easily reproducible.

[ Parent ]

Re: FL inverter (3.00 / 0) (#26)
by dinges on Mon Sep 4th, 2006 at 09:05:48 PM MST
(User Info)

Oops... I thought I was replying this to the thread of Willib. Apparently, the idea of using scanner FL inverters for CFLs is not my own, LOL. I had forgotten that I had read about it here before... Could have sworn it was my very own invention :)

Great minds think alike, I guess.

[ Parent ]

Re: FL inverter (3.00 / 0) (#22)
by dinges on Wed Jul 26th, 2006 at 09:22:08 AM MST
(User Info)

Amanda,

I've got a few old 220V CFLs that are burned out. Usually it's the driver circuit that fails.

The folded up tube themselves have 2 connections at each end, just like FLs.

Could I gut the old 220V electronics from the CFL, put in your FL-driver, and end up with a serviceable 12V CFL? If so, I think I've just found a good use for old defect 220VAC CFLs...

Re: FL inverter (3.00 / 0) (#23)
by dinges on Wed Jul 26th, 2006 at 09:33:34 AM MST
(User Info)

BTW, have read the rest of the story on CCFL, CFL and FL, but I'm still not quite sure whether it should work or not.

And, for clarity, the CFLs (E27 base) that I'm talking about have a total of 4 connections to the actual tube, 2 at each side, just like plain FLs.

[ Parent ]

FL inverter | 26 comments (26 topical, 0 editorial)

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